With the recent progress in office machinery and office automation, the offset lithographic printing system in which the printing plates are made by performing platemaking, or forming images, according to a variety of processes on direct imaging lithographic printing plate precursors that have image receiving layers formed on water-resistant supports has spread throughout the small printing field.
In conventional materials for the direct imaging lithographic printing plates, the image receiving layers are provided on paper supports on which water-resistant layers are coated. In known methods of making the printing plates, lipophilic images are formed on such direct imaging lithographic printing plate precursors by use of oily ink with typewriters or by handwriting and, alternatively, by-hot melt transfer of images from the ink ribbons of heat transfer printers; and non-image areas are then subjected to hydrophilic treatment as needed.
The printing plates thus made, however, fail to have sufficient mechanical strength in image areas or to have sufficient water resistance in paper supports, resulting in swelling or elongation of the printing plates during printing, which causes falling of the image areas.
Platemaking of these direct imaging lithographic printing plate precursors is carried out on ink-jet printers as well. Although water-based ink in which the dispersion medium is water also is used in the platemaking, use of such water-based ink introduces the problems of causing blurs in images on the printing plates and of decreasing drawing speed because the water-based ink dries only slowly. To cope with such troubles, a method of using oily ink in which the dispersion medium is a nonaqueous solvent is disclosed by JP-A-54-117203 (The term "JP-A" as used herein means an "unexamined published Japanese patent application").
However, the introduction of this method often results in clogging the jetting sections of the ink-jet printers with the ink because the ink is jetted from narrow nozzles.